REFLECTOR: NACA scoops and vortex generators

[Velocity Aircraft Owners and Builders list]

I asked about this a couple of weeks ago and thanks for the info.  Someone "dave" posted the following.  Love to see the pictures but cant find them.  If Dave can send them to me that would be most helpful.  I have trouble believing his temperatures, but will take data to support the claims.


David Ullman
N444DX
President EAA 292
541-760-2338
david at davidullman.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Hi Larry - 

All I can do is to tell you of my experience with the roof mounted NACAs. 
I will also (as soon as I can figure out how) post some oil study pictures to the VOBA forum. 

For the first 600 or so hours with my STD-RG I had armpits, and I did get them to work ... acceptably... if you consider CHTs around 400 - 415 acceptable.  Careful management in a climb would keep the CHTs below red line... barely.  That seemed good enough, even though I knew I should be working on better cooling. 

I've written about my cooling misadventures before, but in net what got me working on a better solution had to do with oil cooling issues, not CHTs. 
At the time I was working on cooling drag reduction on my airplane (I was spending a lot of fun time racing with my hangarmate in his really nice Cozy 3 place).  Every drag reduction I did caused my oil temps to get hotter... eventually, I couldn't control them.  Along the way I tried a whole bunch of different cooling setups. Nothing worked.  My oil temp just got worse.  It took close to two years to nail it - it turned out to be three bad cylinders.  It's a long story, and looking back at it, it sure seems obvious that it had to be an engine problem, but at the time I had been working on cooling drag reduction enough to mask the changes in my engine.  Anyway, long (very long) story short, I put the roof mounted NACAs in.

Now... it is important to understand how a NACA works in order to make a NACA work.  In particular, getting the inlet ramp right is really critical.  Square edges along the sides are critical.  There are a bunch of things like that that I see people mess up in NACA installations that preclude them working.  However, if you get them right, they do work, and they work really well.

My coldest CHT now is around 220 - 240, and my hottest is right around 300.  It's arguably too cool... And it's because of the NACAs. 

I'll try to figure out how to post some pictures today.

Thanks again for the article & for your input!

Dave